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Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
52
Biostratigraphy and paleoecology of Cretaceous rocks based
on calcareous nannofossil in Sarayan section, East Iran
Fatemeh Hadavi
1, Marziyeh Notghi Moghaddam
2*, Lida Khodadadi
3
1. Professor, Department of Geology, Ferdowsi University of Mashhad, Mashhad, Iran
2. Assistant Professor, Department of Geology, Payame Noor University, Tehran, I.R of Iran
3. Department of Geology, Payame Noor University, Tehran, I.R of Iran
Received 1 June 2015; accepted 10 January 2016
Abstract
Calcareous nannofossil assemblages recovered from a long, continuous section have been described from the Sarayan region in
Lut Block in east Iran. The marine Upper Cretaceous sediments of this section yield medium diverse and well-preserved calcareous
nannofossil assemblages. A structural analysis of Upper Cretaceous calcareous nannofloras has revealed 30 nannofossil species. A
revised zonation for the Cretaceous is used to subdivide the Cretaceous deposits in this section into five zones (CC21-CC25). Finally,
the paleoecological applications of Upper Cretaceous nannofossils are considered in this section. Surface water temperature,
productivity, and fertility are believed to have been the principal factors controlling species distribution. Warm water indicators such
as Uniplanarius sissinghii, Uniplanarius trifidus, and Micula murus suggest warm surface water conditions in the studied thickness.
In the Sarayan section, based on Lithraphidites carniolensis and Watznaueria barnesae, lower fertility conditions with low
productivity at the Campanian to Maastrichtian were suggested for this region.
Keywords: Biostratigraphy, Paleoecology, Cretaceous, Calcareous nannofossil, Sarayan, Iran
1. Introduction The Upper Cretaceous time-interval represents a
particularly important period for calcareous
nannofossils. During this time, coccolithophorid alge
formed has become an increasingly important
component of marine phytoplankton. This group of
microfossils is very useful for biostratigraphy and
paleoecology studies. Therefore, for the age
determination and investigation of paleoecological
conditions in Lut Block, a detailed study of calcareous
nannofossils samples of the samples from Sarayan
region was performed under an optical microscope. The
Lut Block is under the title of ‘Median Mass of East
Iran’. This basin is a region characterized by the
Jurassic-Cretaceous-Tertiary sequence (Stocklin and
Nabavi 1973). The investigated sequence belongs to the
marl and thin-bedded shale and cobblestone marl
between the shale below and unsorted conglomerate
above. These rocks represent a transect of 316 m that
extents from the eastern margin of the Lut Block in
Sarayan region, which was sampled (Figs. 1 and 2). The
analysis of calcareous nannofossils was carried out on
68 samples.
The aim of this study is to identify the calcareous
nannofossil species, to discuss the standard zonation,
--------------------- *Corresponding author.
E-mail address (es): [email protected]
and to investigate the paleoecological conditions of this
area through the Upper Cretaceous-especially during the
Campanian to Maastrichtian.
2. Geological framework The study area (Sarayan section) is located within the
eastern Lut Block margin, east Iran (Fig. 1). Stocklin
and Nabavi (1973) showed the Lut Block on their
tectonic map of Iran as a separate structural zone and
described it under the title of ‘Median Mass of East
Iran’. They stated that the ‘Lacunar Jurassic-
Cretaceous-Tertiary’ sequence of similar facies are
similar to that in central Iran, but sub-horizontal to
gently warped and faulted, presumably resting on a rigid
substratum consolidated in late Triassic and/or even
earlier time. The investigated sedimentary interval spans
from samples S1-S89 and consists mostly of shale, marl,
and thin bedded shale and cobblestone marl between the
shale below and pink coloured unsorted conglomerate
above (Fig. 2). The thickness of these sediments is
356m.
3. Material and methods The material examined and described in this paper is
taken from the released well section. Eighty-nine
samples were collected from the Sarayan section,
sampled at intervals from 4m. For the nannofossils,
smear slides were prepared using the technique of Bown
Islamic Azad University
Mashhad Branch
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
53
Fig. 1 Sample locality of Sarayan section. With changes of in the Grimonj map (1:100000) (after Amidi and Navai, 2005)
and Young (1998) and examined under a light
microscope at 1,000 magnification by both cross-
polarized and phase-contrast methods. All calcareous
nannofossil specimens encountered were identified
following the taxonomic schemes of Cepek and Hay
(1969), Thierstein (1976) Perch-Nielsen (1985), Burnett
(1998), and Young (1999) (Figures 3–7).
The assemblages were qualitatively and semi-
quantitatively characterized in terms of preservation and
abundance.
The total abundance of Calcareous nannofossil was
estimated as the number of specimens for the field of
view. For the paleoecological studies and because of
low abundance of nannofossils in the studied samples,
all nannofossil species were counted in 10 purviews.
Next, the percentages of each species for drawing the
diagrams were calculated (Table 1).
4. Previous investigation The earliest paleontological studies of the Cretaceous
deposits of the Lut Block focused on foraminifera (e.g.,
Babazadeh et al. (2010)). Some sedimentology
investigations, magmatic evolution, and tectonic
evolution, have also been conducted by Babazadeh et al.
(2010), Saadat et al. (2010), Mazhari and Sharifiyan
Attar (2012), and Asadi and Kolahdani (2014).
Previous nannofossil studies of Cretaceous deposits in
Lut Block were by Hadavi et al. (2012) in the Gazak
section (east Birjand).
In the present study, the nannofloras of the Sarayan
region were discussed for the first time, and
biostratigraphy and paleoenvironmental conditions
across Campanian to Maastrichtian of this basin were
deliberated.
5. Results 5.1. Nannofossils preservation
Dissolution and diagenesis can strongly alter the
preservation of calcareous nannofossil assemblage.
These factors can severely affect their application to
paleoenvironmental reconstructions (Honjo, 1976;
Steinmetz, 1994; Andruleit, 1997). The percentage of
the dissolution of resistant nannofossil species and the
percentage of the total calcareous nannofossil
abundance were used to assess preservation (Williams
and Bralower, 1995). In 89 samples from the Sarayan
section, the nannofossils are not affected by etching;
delicate structures are, however, still preserved but
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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Fig. 2: Lithostratigraphic column of the Sarayan section.
significantly affected by secondary calcite overgrowth
and some coccolith central structures sometimes tend to
be lightly overgrown. Many authors use the percentage
of the robust form of W. barnesae, which is less
susceptible to dissolution, to assess the impact of the
diagenesis. According to Roth and Krumbach (1986),
assemblages containing less than 40% of W. barnesae
are thought to be only slightly altered by diagenesis and
can be used as primary signal. In this study, the
abundance of W. barnesae varies in most cases from
10% to 64% in Table 1.
In conclusion, it is reasonable to think that the
calcareous nannofossil assemblages of this section
reflect a primary signal and can therefore be used as
paleoenvironmental proxies to reconstruct the surface
water conditions of the Lut Block basin.
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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Tab
le 1: A
bun
dan
ce chart o
f the id
entified
calcareou
s nan
no
fossil sp
ecies in th
e Saray
an sectio
n.
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Tab
le 1: C
ontin
ued
.
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Tab
le 1: C
ontin
ued
.
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
58
Tab
le 1: C
ontin
ued
.
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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Figure 3: Nannofossil pictures of the studied sections (All figures light micrographs magnified X1000)
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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Figure 4: Nannofossil pictures of the studied sections (All figures light micrographs magnified X1000)
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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Figure 5: Nannofossil pictures of the studied sections (All figures light micrographs magnified X1000)
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Figure 6: Nannofossil pictures of the studied sections (All figures light micrographs magnified X1000)
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Figure 7: Nannofossil pictures of the studied sections (All Figures light micrographs magnified X1000)
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
64
5.2. Nannofossils diversity and abundance
In the present study, 30 species belonging to 21 genera
of calcareous nannofossils in the Sarayan section were
identified. These nannofossils are of well-to-moderate
diversity and moderate-to-relatively high in abundance.
The abundance of nannofossils in different samples
does not follow a general pattern as some species tend
to increase or decline from the base to top section—for
example W. barnesae increases towards the top of these
sections, while Micula decussata decreases along the
same path (Table 1).
The most dominant species are W. barnesae with an
average of 24.17%, Q. sissinghii with an average of
26.29%, Q. trifidum with an average of 7.76%,
Calculites obscurus with an average of 6.22%, and
Lucianorhabdus cayeuxii with an average of 14.41% in
the Sarayan section.
Some Cretaceous nannofossil genera like Marthastrites,
Aspidolithus, Braarudosphaera, and Acuturris are
present in these samples, but occur only sporadically
with relatively low percentages. Some species are rare,
and they were identified only from the uppermost part
of the studied sections such as M. murus, and
Arkhangelskiella cymbiformis (Table 1).
5.3. Calcareous nannofossil zonation Calcareous nannofossils are one of the primary fossil
groups used in Mesozoic biostratigraphy because of
their abundance, rapid rate of evolution, and planktonic
nature that allows a wide dispersal throughout the world
oceans (Bown, 1998). The calcareous nannofossil
zonation of the Cretaceous (especially the Upper
Cretaceous) is well advanced. The biostratigraphic
zonation scheme used for the Upper Cretaceous
sediments follows (Sissingh, 1977) as modified and
illustrated in Perch-Nielsen (1985). For the Cretaceous,
the first and last occurrence (FO; LO) of species are
mainly used for subdivision and zonation.
Table 2 illustrates diagrammatically the most important
Upper Cretaceous calcareous nannofossil zonations
proposed in the Sarayan section. In this section, six bio-
events are documented in the Sarayan section: the FO of
Uniplanarius sissinghii, the FO of Uniplanarius trifidus,
the LO of Reinhardites anthophorus, the LO of
Tranolithus phacelosus, the LO of Reinhardites levis,
and the FO of M. murus (Table 2). According to the FO
and LO of marker species, five calcareous nannofossil
biozones were recognized in Sarayan section—ranging
in age from early Late Campanian to Late
Maastrichtian. The proposed biozones arranged from
base to top are Uniplanarius sissinghii, Uniplanarius
trifidus, Tranolithus phacelosus, Reinhardites levis, and
Arkhangelskiella cymbiformis zones.
Quadrum sissinghii zone (CC21)
The Q. sissinghii zone was proposed by Sissingh
(1977). The age of this zone is early Late Campanian.
The zone is explained as the interval from the FO of Q.
sissinghii to the FO of Q. trifidum by Sissingh (1977).
This is the oldest identified zone in the Sarayan section.
The most dominant species in this zone are Calculites
obscurus, Eiffellithus gorkae, L. cayeuxii, W. barnesae, Watznaueria biporta, and R. anthophorus. The
thickness of this biozone is 88 m.
Quadrum trifidum zone (CC22)
The Q. trifidum zone (CC22) was proposed by Bukry
and Bramlette (1970), emended by Sissingh (1977). The
age of this zone is late Late Campanian. It is identified
as the interval between the FO of Q. trifidum to the last
occurrence (LO) of R. anthophorus. It is dominated,
besides the marker species, by C. obscurus, E. gorkae,
L. cayeuxii, Lucianorhabdus maleformis, M. decussata,
Q. gothicum, R. anthophorus, W. barnesae, and W.
biporta. The thickness of this zone is 92m.
Tranolithus phacelosus zone (CC23)
This zone, also named CC23, was described by Sissingh
(1977); it includes the interval from the LO of R.
anthophorus to LO of T. phacelosus. The age of this
zone is latest Campanian to Early Maastrichtian. In this
zone, the most dominant species, in addition to the
marker species, are C. obscurus, L. cayeuxii, M.
decussata, Q. gartneri, W. barnesae, and W. biporta.
The thickness of this studied biozone is 96m.
Reinhardtites levis zone (CC24)
This zone (CC24) was proposed by Sissingh (1977) and
is identified from LO of T. phacelosus to the LO of R.
levis. Early Maastrichtian is the age of this zone. It is
dominated, besides the marker species, by C. obscurus,
Calculites ovalis, E. gorkae, L. cayeuxii, M. decussata,
W. barnesae, and W. biporta.
The thickness of this biozone is 40m.
Arkhangelskiella cymbiformis zone (CC25)
The A. cymbiformis zone was proposed by Perch-
Nielsen et al. (1982) and later emended by Sissingh
(1977). The age of this zone is Late Maastrichtian. This
zone is identified from the LO of R. levis to the FO of
Nephrolithus frequens. In low latitudes, this zone is
identified from the LO of R. levis to the FO of M. murus
(Perch-Nielsen, 1972). In this section, N. frequens was
not found and the FO of M. murus was used for the
identification of the upper boundary of CC25. The most
dominant species in this zone, besides the marker
species, are C. obscurus, Ceratolithoides aculeus, E.
gorkae, L. cayeuxii, W. barnesae, and W. biporta. The
Thickness of A. cymbiformis zone is 40m.
According to this study and also based on the calcareous
nannofossil biostratigraphy, especially given the
recognition of CC21-CC26 from the Sarayan section,
the age of the sequence in the studied region was
suggested early Late Campanian to Late Maastrichtian.
6. Discussion 6.1. Paleoecological features of the Sarayan section
Calcareous nannofossils include the coccoliths and
coccospheres of haptophyte algae as well as the
associated nannoliths that are of unknown provenance.
Their calcareous skeletons are found in marine deposits
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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often in vast numbers, sometimes making up the major
component of a particular rock such as the chalk. The
first recorded occurrences of calcareous nannofossils
(nannoliths) are from the late Triassic (Carnian) (Bown
and Young, 1998). Nannofossils are widespread in the
present oceans, from coastal areas to open ocean
settings, and constitute a large part of marine
phytoplanktonic communities. Investigation of
paleoecological conditions in Mesozoic, particularly
Upper Cretaceous based on calcareous nannofossils, has
been performed, by many authors (Sissingh 1977; Lees,
2002; Bornemann et al., 2003; Erba, 2004, 2006;
Shamrock and Watkins, 2009). The distribution of
calcareous nannoplankton in the current study is used to
investigate the Paleoecological conditions in the studied
region.
Tab
le 2: R
ang
e chart sh
ow
ing
the d
istribu
tion o
f calcareou
s nan
no
fossil sp
ecies record
ed in
the S
arayan
section.
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Figure 8: Abundance chart of Watznaueria barnesae in the Sarayan section
Figure 9: Abundance chart of Micula decussata in the Sarayan section
The common occurrences of the relatively eutrophic
taxa Zeugrhabdotus erectus and Biscutum constans as
well as of the cold-water species indicate high nutrient
contents and cool surface water conditions during the
deposition of the sequence. In the Cretaceous sediment,
the species of Eiffellithus spp., Prediscosphaera spp.
species (except Prediscoshphaera stoveri),
Lithraphidites spp., Microrhabdulus spp., and W.
barnesae are known as indicators of low productivity
(Herrle et al., 2003; Friedrich et al., 2005). In the
studied area, probably a low productivity level
prevailed-this assumption is supported by the character
of the nannofloral assemblages dominated by Tethyan
taxa such as Lithraphidites carniolensis and W.
barnesae.
In Upper Cretaceous, some taxa are more related to
higher paleolatitudes with cold surface water, such as
Biscutum ellipticum, Kamptnerius magnificus,
Gartnerago segmentatum, and Ahmuellerella regularis
(Erba et al., 1995; Svabenicka, 1999; Melinte and
Lamolda, 2002; Aguado et al., 2005). In Upper
Cretaceous, some nannofossils, such as Ceratolithoides
aculeus, Uniplanarius sissinghii, Uniplanarius
trifidusrefer, are used to warm surface water (Bukry,
1973; Wind and Wise, 1983; Watkins, 1992; Watkins,
1996; Watkins et al., 1996).
Hadavi et al. / Iranian Journal of Earth Sciences 8 (2016) / 52-68
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This is mirrored in the composition of the calcareous
nannoplankton assemblages from the studied section,
which contain low-to-middle latitude species such as
Ceratolithoides aculeus, Uniplanarius sissinghii,
Uniplanarius trifidus. The common occurrence within
the Campanian to Maastrichtian of the studied region, of
species belonging to the genus Watznaueria is
indicative not only of a warm climate, but also of a low-
latitude setting.
Some earlier researchers reported that M. decussata is
becoming more abundant with an increasing depth, and
W. barnesae is one of the most dominant species that
shows a strong inverse correlation with depth
(Thierstein, 1976; Thierstein, 1981). In the studied
section, W. barnesae increases towards the top of this
section and, conversely, M. decussata declines (Figures.
8 and 9). On the other hand, these observations indicate
decreases in depth from the base to top of the Sarayan
section. These results match well with lithological
changes in the Lithostratigraphic column of this section.
7. Conclusions In this study, 30 species and 21 genera were identified
in the Sarayan section. The analysis of calcareous
nannofossils revealed the presence of Campanian-
Maastrichtian marine sediments in the eastern Lut Block
margin. The nannofossil assemblages of the Sarayan
section have relatively well-to-moderate preservation.
The studied sediments in Sarayan region belong to
Zones CC21-CC25 (Sissingh, 1977) on the basis of the
first occurrence and last occurrence of Q. sissinghii, Q.
trifidum, R. anthophorus, T. phacelosus, R. levis, and M.
murus, respectively. The attribution of these biozones
permits us to access an age of early Late Campanian to
Late Maastrichtian for the studied section. Paying
attention to the increased W. barnesae and decreased M.
decussate from base to top as well as lithological
changes (marl towards conglomerate) of the Sarayan
section suggest a decline in depth towards the top of this
section. Index calcareous nannofossil species at the
studied sediments indicate low nutrients in relation to
mesotrophic conditions and show that the basin of this
sediments is in a low latitude with warm temperature.
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